[The Might]

ME is NOT a state, so the whole idea of it being one big democracy makes little or no sense.
Gondor, Rohan, The Shire, these could perhaps eventually become democracies, but not all of Middle-earth.

As far as demography, and not democracy, is concerned, I doubt any clear figures can be given.
Still, it is pretty certain that out the inhabitants of Middle-earth, and by this term I am talking about the whole continent, and not only its north-western part, would be supporters of Sauron. It is stated in many places that many tribes of Men had been enslaved by him in the East, so the numbers of his followers, not only the Orcs, would be quite high.